This invention relates to telephone systems in which communication is effected via a radio link.
The provision of telephone communication by radio is a standard facility provided by a number of developed countries. However, connections between subscribers are generally manually made and monitored by an intervening operator. Efforts have been made to provide automatic access to and from a public automatic switched network, but reliable operation demands absolute integrity of establishing, maintaining and subsequently releasing the connection irrespective of signal fluctuations or the presence of noise in the radio channel. The known techniques rely on the transmission of coded tones to provide the control signals associated with the connection to and from the respective radio stations.
Known systems which enable direct connection with a switched telephone network use techniques which are similar to those commonly found in line communication. Whilst these techniques provide a working system, certain limitations inherent in their implementation preclude the optimum use of a radio link.